The invention relates to a seal for sealing a sealing surface between two machine parts that move relative to each other, wherein a seal body of the seal comprises a retaining part, disposed toward the groove base in a groove in one of the machine parts, a sealing part, disposed in the groove facing the sealing surface, and a resilient connector part between the sealing part and the retaining part, and wherein the seal has a recess between the retaining part and the connector part and a further recess between the connector part and the sealing part, and a seal arrangement, wherein the seal is disposed in a groove in one of two machine parts that can move relative to each other.
Such seals have a basic cross-sectional form in the shape of an S or Z, the recesses being formed by this basic shape. The seals are usually manufactured in one piece from a rubber-elastic material, e.g. polyurethane or rubber and constituted as a sealing ring with radial symmetry. In this embodiment, the seals can be used as rod or piston seals for sealing pneumatic applications, e.g. pneumatic cylinders or valves, and/or as rotation seals, e.g. in high-pressure applications.
Such a seal is usually inserted between two machine parts that move axially and/or in a rotary fashion with respect to each other, in a groove in a surface of one of the machine parts, this surface being disposed opposite a sealing surface constituted by a surface of the second machine part. Between these surfaces there is therefore a sealing gap to be sealed. In the case of a sealing ring, the two surfaces are concentrically disposed with respect to one another. Normally, in the case of a piston seal, the groove is disposed inside the machine part; in the case of a rod seal, the groove is disposed on the outer surface of the machine part. The resilient connector part acts as a spring between the sealing part, usually comprising at least one sealing lip, and the retaining part. The retaining part is dimensioned so as to enable a seating of the seal on the base of the groove which is as immobile as possible.
When such a seal is used, e.g. in a pneumatic cylinder, a medium that is under pressure, i.e. a fluid, e.g. oil and/or air, that is in a pressure compartment is reciprocally applied to the seal. To achieve the desired sealing effect, the seal is inserted into the groove prestressed. This compresses the seal to such an extent that the resilient action of the connector part presses the surface of the sealing part that is disposed toward the sealing surface, against the sealing surface. In the case of a sealing ring, the sealing ring is radially compressed. The pressure in the recesses of the seal is activated when the medium is applied. Because the medium under pressure flows into the recesses, the sealing part is pressed against the sealing surface in addition to the spring action of the connector part. For this purpose, such a seal is inserted into the groove with spacing between its surfaces that face the walls of the groove (lateral surfaces) and the groove walls. The medium is therefore free to flow into the recesses between the groove walls and the lateral surfaces.
The recess adjacent to the sealing part can result in malfunctions during operation, e.g. of a pneumatic cylinder. The sealing part can tip over in the groove in response to forces exerted on the seal during movement of the machine parts, which are sealed against each other by means of the seal and/or due to the alternating pressure of the medium. If this is the case then, given a pressure p1 exerted on one of the lateral surfaces, pressure p2 built up on the opposite side, i.e. on the second lateral surface, can cause the seal to lift away from the sealing surface. If this loosening occurs, the sealing effect is no longer achieved. This malfunction is termed seal blow-by. The sealing function can only be restored by removing the pressure from both lateral surfaces.
The EP 0 906 528 B1 discloses a seal of this kind that is constituted as a sealing ring, wherein precautions against blow-by have already been taken. For this purpose, the sealing ring has radial pressure equalization ducts that allow the media on both sides of the sealing ring to flow into the recesses of the sealing ring. However, the radial pressure equalization ducts cannot prevent the sealing part from tipping over.
In some cases, therefore, such seals are installed having been pressed on a block, i.e. the seals are so greatly compressed, radially in the case of sealing rings, that the recesses are filled by the intermediate part, i.e. are practically no longer able to perform their function in the installed condition, i.e. they do not permit pressure activation. In this case, tipping over of the section of the seal is prevented in the dynamic sealing region but the functional behavior of the seal is adversely affected to a great extent and friction is increased.
The object of the invention is to provide a seal and a seal arrangement that avoid the disadvantages of the prior art and, in particular, the occurrence of the malfunction of blow-by while retaining good sealing function in all installation situations.